Surgically implanted cardiac pacing systems, such as pacemakers and defibrillators, play an important role in the treatment of heart disease. In the 50 years since the first pacemaker was implanted, technology has improved dramatically, and these systems have saved or improved the quality of countless lives. Pacemakers treat slow heart rhythms by increasing the heart rate or by coordinating the heart's contraction for some heart failure patients. Implantable cardioverter-defibrillators stop dangerous rapid heart rhythms by delivering an electric shock.
Cardiac pacing systems typically include a timing device and a lead, which are placed inside the body of a patient. One part of the system is the pulse generator containing electric circuits and a battery, usually placed under the skin on the chest wall beneath the collarbone. To replace the battery, the pulse generator must be changed by a simple surgical procedure every 5 to 10 years. Another part of the system includes the wires, or leads, which run between the pulse generator and the heart. In a pacemaker, these leads allow the device to increase the heart rate by delivering small timed bursts of electric energy to make the heart beat faster. In a defibrillator, the lead has special coils to allow the device to deliver a high-energy shock and convert potentially dangerous rapid rhythms (ventricular tachycardia or fibrillation) back to a normal rhythm. Additionally, the leads may transmit information about the heart's electrical activity to the pacemaker.
For both of these functions, leads must be in contact with heart tissue. Most leads pass through a vein under the collarbone that connects to the right side of the heart (right atrium and right ventricle). In some cases, a lead is inserted through a vein and guided into a heart chamber where it is attached with the heart. In other instances, a lead is attached to the outside of the heart. To remain attached to the heart muscle, most leads have a fixation mechanism, such as a small screw and/or hooks at the end.
Within a relatively short time after a lead is implanted into the body, the body's natural healing process forms scar tissue along the lead and possibly at its tip, thereby fastening it even more securely in the patient's body. Leads usually last longer than device batteries, so leads are simply reconnected to each new pulse generator (battery) at the time of replacement. Although leads are designed to be implanted permanently in the body, occasionally these leads must be removed, or extracted. Leads may be removed from patients for numerous reasons, including but not limited to, infections, lead age, and lead malfunction.
Removal or extraction of the lead may be difficult. As mentioned above, the body's natural healing process forms scar tissue over and along the lead, and possibly at its tip, thereby encasing at least a portion of the lead and fastening it even more securely in the patients body. In addition, the lead and/or tissue may become attached to the vasculature wall. Both results may, therefore, increase the difficulty of removing the leads from the patient's vasculature.
A variety of tools have been developed to make lead extraction safer and more successful. Current lead extraction techniques include mechanical traction, mechanical devices, and laser devices. Mechanical traction may be accomplished by inserting a locking stylet into the hollow portion of the lead and then pulling the lead to remove it. An example of such a lead locking device is described and illustrated in U.S. Pat. No. 6,167,315 to Coe et al., which is hereby incorporated herein by reference in its entirety for all that it teaches and for all purposes.
A mechanical device to extract leads includes a flexible tube called a sheath a passes over the lead and/or the surrounding tissue. The sheath typically may include a cutting blade, such that upon advancement, the cutting blade and sheath cooperate to separate the scar tissue from other scar tissue including the scar tissue surrounding the lead. In some cases, the cutting blade and sheath may also separate the tissue itself from the lead. Once the lead is separated from the surrounding tissue and/or the surrounding tissue is separated from the remaining scar tissue, the lead may be inserted into a hollow lumen of the sheath for removal and/or be removed from the patient's vasculature using some other mechanical devices, such as the mechanical traction device previously described in United States Patent Publication No. 2008/0154293 to Taylor, which is hereby incorporated herein by reference in its entirety for all that it teaches and for all purposes.
Some lead extraction devices include mechanical sheaths that have trigger mechanisms for extending the blade from the distal end of the sheath. An example of such devices and method used to extract leads is described and illustrated in U.S. Pat. No. 5,651,781 to Grace, which is hereby incorporated herein by reference in its entirety for all that it teaches and for all purposes.
Controlling the extension of the blade within a patient's vasculature may be critical, particularly when the sheath and blade negotiate tortuous paths that exist in certain vascular or physiological environments. Furthermore, in certain cases, using such mechanical devices for lead removal may require more precise control, such as when the leads are located in, and/or attached to a structurally-weak portion of the vasculature. For instance, typical leads in a human may pass through the innominate vein, past the superior vena cava (“SVC”), and into the right atrium of the heart. Tissue growth occurring along the SVC and other locations along the innominate vein may increase the risk and difficulty in extracting the leads from such locations, particularly when the vein(s)′ walls are thin. Tissue growth may also occur at other challenging locations within a patient's vasculature which requires the delicate and precise control of the devices used to extract leads from such locations.